The present invention relates to a scroll-type fluid machine and, more particularly, to a scroll member which ensures a higher precision of machining of the spiral wrap on the scroll member.
Various contours of a wrap for scroll members have been proposed, and a typical example is a spiral contour as proposed in U.S. Pat. No. 4,464,100. The design of this wrap, as well as other known wraps having spiral forms, does not take into account the machinability of the side surfaces of the wrap and the surface of the groove between adjacent turns of the warp, i.e., the surface of the end plate of the scroll member.
In general, the spiral wrap is formed along an involute curve or a combination of an involute curve and other curves such as arcs.
It is true that the wrap side surfaces and the groove bottom surface of the same scroll member can be simultaneously machined. Such a machining method, however, is impractical in that the dimensional precision of the wrap is adversely affected by, for example, wear of the machining tool. It has been determined that it is more practical in view of the wear of machine tools and so forth to machine the wrap side surfaces and the groove bottom surface independently and separately.
The contour of the wrap is determined in consideration of both the function of the wrap and easiness of machining of the same. However, the contour of the wrap side surfaces has been the first consideration in fact and then the contour of the groove bottom surface has been determined in conformity with the contour defined between adjacent turns of the wrap. This inevitably requires the machine tool to be moved a long distance along a complicated path, resulting in a long machining time. Additionally, it is not possible to machine the entire portion of the groove bottom surface in one machining cycle, because an unmachined portion remains such as for example, the starting end region of the wrap. Consequently, the precision is adversely affected due to a duplicated machining of the same surface.